1. Field of the Invention
The present invention relates to a vacuum interrupter and, more particularly, to a contact assembly for a vacuum interrupter having excellent mechanical tolerance against a mechanical impact of contacts according to switching the contacts.
2. Description of the Related Art
A vacuum interrupter is a switching contact and arc-extinguishing unit used as a core component of an electric power device such as a vacuum circuit breaker, a vacuum switch, a vacuum contactor, or the like, in order to break an electric load current or a fault current in an electric power system.
Among such application devices of the vacuum interrupter, the vacuum circuit breaker serves to protect an electric load in power transmission controlling and the electric power system, and since the vacuum circuit breaker has many advantages that it has a large breaking capacity (voltage/current) and high operational reliability and stability and can be mounted in a small space, the vacuum circuit breaker has been extensively applied in voltage environments from a middle voltage to a high voltage. Also, the breaking capacity of the vacuum circuit breaker is proportionally increasing in line with the increase in the size of industrial facilities.
A configuration example of the vacuum interrupter in a vacuum circuit breaker will be described with reference to FIG. 1 as follows.
As shown in FIG. 1, generally, a vacuum interrupter 10 comprises an insulating container 9 made of a ceramic material having excellent electrical insulating properties and heat resistance and having open upper and lower portions, a fixed electrode 4 insertedly positioned in the insulating container 9 and having one end portion to which a fixed contact 3 is coupled through, for example, welding and the other end portion electrically connected to, for example, an electric power source, and a movable electrode 1 insertedly positioned in the insulating container 9 and having one end portion to which a movable contact 2 is coupled through, for example, welding and the other end portion electrically connected to, for example, an electrical load. Reference numeral 5 designates an air-tight bellows made of a metal and movably supporting the movable electrode 1, and reference numeral 6 designates a shielding plate installed at the movable electrode 1 to shield and protect the air-tight bellows 5 against arc. Reference numeral 7 designates a first seal cup welded to the insulating container 9 so as to be fixedly installed to hermetically close a gap between the lower open portion and the movable electrode 1. Reference numeral 8 designates a second seal cup welded to the insulating container 9 so as to be fixedly installed to hermetically close a gap between the upper open portion and the fixed electrode 4. Reference numeral 10 designates a central shielding plate installed at the center of the insulating container 9 in order to protect an inner wall face of the insulating container 9 against arc.
The general vacuum interrupter 10 configured as described above may be connected to an actuator including a driving source (not shown) such as a spring or a motor and a link mechanism 13. The movable electrode 1 may be electrically connected with an electric power line (circuit) of the load side through a terminal 12, and the fixed electrode 4 may be electrically connected with an electric power line (circuit) of an electrical power source side through a terminal 11.
In FIG. 1, reference numeral 14 designates an outer case of the vacuum circuit breaker and reference numeral 15 designates wheels for moving the vacuum circuit breaker.
In FIG. 1, when the movable electrode 1 is lifted according to a transmission of driving force (or power) from the link mechanism 13 of the actuator, the movable contact 2 installed at one end portion of the movable electrode 1 is brought into contact with the fixed contact 3, causing the power source electrically connected to the movable electrode 1 through the terminal 12 and the load electrically connected to the fixed electrode 4 through the terminal 11 to be connected into an operational state in which the electric power circuit becomes a closed circuit.
In FIG. 1, when the movable electrode 1 is lowered according to transfer of driving force from the actuator including the driving source (not shown) such as a spring or a motor and the link mechanism 13, the movable contact 2 installed at one end portion of the movable electrode 1 is separated from the fixed contact 3, electrically disconnecting the electrical load electrically connected with the movable electrode 1 and the electrical power source electrically connected with the fixed electrode, into an operation state in which the circuit is open.
In the operation of closing the circuit, as shown in FIG. 2, current I flows through the movable electrode 1, the movable contact 2, the fixed contact 3, and the fixed electrode 4. In FIG. 2, reference numerals 3a and 2a designate splash shields for protecting a rear portion of the contacts against metal vapor of an arc generated when the contacts are open.
In case in which the movable contact 2 and the fixed contact 3 has a spiral shape, an arc generated between the movable contact 2 and the fixed contact 3 when the movable contact 2 and the fixed contact 3 are open is pushed to an outer side, upon receiving force (F) in FIG. 2, which is called Lorentz force according to Fleming's left hand rule, by a current flow in a vertical direction and a corresponding horizontal magnetic field, rotated to be dispersed and become extinct,
Meanwhile, in case of the related art vacuum interrupter as described above, both the movable contact 2 and the fixed contact 3 receive mechanical stress during opening and closing operation. In particular, in the case of the vacuum interrupter employing a spiral contact structure, as shown in FIG. 3, a horizontal sectional area of a contact portion SA at the fixed electrode 4 and the movable electrode 1 supporting a lower end portion of the contact is preferably required to be smaller than a contact area (i.e., the area of the contact portion with which the movable contact or the fixed contact is brought into contact) at the movable contact 2 or the fixed contact 3 in order to obtain stronger Lorentz force (F) for driving arc in the horizontal direction at an initial stage of cutting off (or breaking) a fault current, which is, then more advantageous to cut off (or break) a large current. This is because, as the difference between the contact area at the movable contact 2 or the fixed contact 3 and the horizontal sectional area of the movable electrode 1 or the fixed electrode 4 is increased, Lorentz force (F) at the initial stage of opening the contacts is increased.
However, in case of the contact area of the contacts, there is a limitation in increasing the contact area to secure an insulating distance from an internal component such as the central shielding plate 10, or the like, of the vacuum interrupter. Also, the increase in the sectional area of the fixed electrode 4 and the movable electrode 1 supporting the contact lower end portion is also inevitably limited.
For those reasons, when the related art vacuum interrupter performs closing operation, the mechanical stress according to the contact impact between the contacts is applied to the movable contact 2 and the fixed contact 3, causing the contacts to be mechanically deformed.
When operating energy is increased in order to break the large current, the contact portions are severely deformed in proportion to the increased closing energy, which leads to a possibility in which the original function (insulation, arc-extinguishing, and electrical connection) of the vacuum interrupter is damaged.
Thus, reinforcing of the strength of the contact portions of the vacuum interrupter according to the increase in the capacity of the vacuum circuit breaker is urgently required.